Higher Relative Water Content Research Articles

Screening for drought tolerance potential of nine cocoa (Theobroma cacao L.) genotypes from Ghana

This study was conducted with a view to screen nine genotypes of Cacao from The Cocoa Research Institute of Ghana (CRIG) to test their abilities to withstand drought stress conditions using parameters such as leaf relative water content (RWC), proline accumulation in leaves and trichomes. The experimental design consisted of three replicates of the genotypes used and these were laid out in Complete Randomized Block Design (CRBD) to determine the drought tolerance potentials of the nine genotypes of cocoa at the seedling stage. Two water treatments were used which involved withholding water from one day after full saturation with water prior to the first appearance of drought symptoms (FADS) and watering every two days to the completion of the experiment. Results in this research revealed that proline was found to gather in water-stressed seedlings, and the differences in the mean proline amounts in the genotypes was found to be significant. Genotype T63/971 x Sca9 had the most elevated concentration of free proline at FADS (4 μg/g DW) followed by genotype T60 x Pound10 (3.5 μg/g DW) whereas genotype PA150 × 9006 had the smallest amount of accumulated proline in leaves. Genotype PA150 × 6020 had the highest RWC and SMC of 65% and 1.5% respectively at FADS whilst genotype PA7 x 6035 had the lowest RWC of 43%. There was a direct relationship between the amounts of free proline of genotypes T63/971 x SCA9 and T60 x POUND10 and their respective RWC of the leaves. Genotypes T63/971 x SCA9 and PA150 × 9006 had the highest and lowest numbers of trichomes respectively. Inference from this study revealed that T63/971 x SCA9 and T60 x POUND10 genotypes appear to be the most drought-tolerant genotypes in view of their relatively high values of free proline content, leaf RWC, trichomes and lower values of soil water use (SMC).

Root endophytic fungus Piriformospora indica and zinc attenuate cold stress in grapevine by influencing leaf phytochemicals and minerals content

The effects of Piriformospora indica (Pi) inoculation and zinc (Zn) soil- application on mitigation of cold stress in grapevine (Vitis vinifera L. cv Sultana) plants were investigated. Fungal mycelium (1% w/v) suspension was added to each cutting and Zn (5.0 mg/l Zn-EDTA) applied to each pot every 15 day. At the end of experiment, half of the pots (control and Pi and Zn-treated vines) were subjected to 4 °C for 24 h. The remaining vines in each treatment group were kept at 24 °C. Cold stress (4 °C) markedly decrease leaf photosynthetic pigments and relative water content however, Pi and Zn resulted in higher stability of photosynthetic pigments and higher relative water content in treated vines compared to control vines. Cold stress increased leaf electrolyte leakage (EL), lipid peroxidation and hydrogen peroxide contents in vines, whereas Pi colonization and Zn treatments considerably reduced their levels. Moreover, leaf superoxide dismutase, catalase, guaiacol peroxidase, and ascorbate peroxidase activities markedly increased in Pi- and Zn-treated vines under cold stress. Decreasing the temperature from 24 to 4 °C increased leaf abscisic acid (ABA), polyamines (PAs), soluble carbohydrate, proline, soluble proteins and total phenol content in all vines. However, vines treated with Pi + Zn showed marked increases in these compounds compared to control vines under cold stress. The leaf nutrient content of vines under low temperature stress decreased compared to those grown at 24 °C. However, this decrease in leaf nutrient was affected lesser in vines inoculated with Pi and Zn. Therefore, application of Pi and Zn allowed chilled vines to absorb higher nutrient during normal temperatures, enabling them to attenuate cold stress by increase in osmoregulants, antioxidant enzymes activity and plant growth regulators (ABA and PAs) in their tissues.

Disease Severity, Resistance Analysis, and Expression Profiling of Pathogenesis-Related Protein Genes after the Inoculation of Fusarium equiseti in Wheat

Wheat (Triticum aestivum) is an important cereal crop, grown throughout the temperate and in some tropical and sub-tropical zones, at higher elevations. Several biotic and abiotic factors influence the production of wheat. In the present study, two wheat varieties have been subjected to disease severity and resistance analysis against Fusarium equiseti. Disease severity analysis revealed Shafaq-2006 to be more resistant than Sahar-2006. Both varieties were further subjected to the expression analysis of six important defense-related genes by RT-PCR and quantitative real-time PCR. This analysis revealed that PR-1, TLP, Chitinase, and β-1,3-glucanase genes were highly expressed in Shafaq-2006 and possibly play a significant role in its defense mechanism. In addition, biochemical and physiochemical parameters were also studied to further explore the difference between resistant and susceptible varieties. With total proline and protein contents, sugar and chlorophyll contents also increased significantly in resistant variety. Likewise, higher relative water content, total plant length, and the high root–shoot ratio was observed in resistant plants, compared to susceptible wheat plants. These increases in chemical and physiological parameters might be related to the activation of the defense mechanism due to the higher expression of PR genes in the resistant wheat variety. These genes can further be employed for cloning into wheat and other transgenic crops to develop resistance against F. equiseti.

Morphological and Physio-Biochemical Responses of Watermelon Grafted onto Rootstocks of Wild Watermelon [Citrullus colocynthis (L.) Schrad] and Commercial Interspecific Cucurbita Hybrid to Drought Stress

This study aimed to assess the morphological and physio-biochemical responses of a commercial watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) cv. ‘Crimson Sweet’ grafted onto a drought-tolerant rootstock of wild watermelon (bitter apple, Citrullus colocynthis (L.) Schrad, ‘Esfahan’) in comparison with an ungrafted ‘Crimson Sweet’ watermelon or one grafted onto a commercial interspecific Cucurbita hybrid (Cucurbita maxima Duch. × Cucurbita moschata Duch.) rootstock (‘Shintoza’) under water stress. The experiment was conducted in pots under a controlled environment in a greenhouse, and water stress was imposed by maintaining moisture level in pots at 100% (well water (WW)) or 50% (water deficit (WD)) of container capacity (CC). WD significantly decreased most of the morphological traits in ungrafted and grafted plants, while the decrease in growth traits was lower in grafted plants than ungrafted plants. The response of grafted plants onto wild watermelon rootstock (‘Esfahan’) for most of the affected parameters (shoot fresh and dry weight, vine length and internodal length) was, however, comparable to those grafted onto commercial Cucurbita hybrid rootstock (‘Shintoza’). Plants grafted onto bitter apple (wild watermelon) exhibited a relatively lower decrease in growth and biomass, besides showing higher antioxidant activity (e.g., guaiacol peroxidase) concomitant with the lower accumulation of malondialdehyde and electrolyte leakage in the leaf tissues in comparison with ungrafted plants. The overall growth performance, as well as those under water stress conditions in commercial rootstock-grafted watermelon, was related to its better plant water status (e.g., high relative water content) which was likely ascertained by its greater root efficiency. This suggests that watermelons grafted onto bitter apple rootstock and Cucurbita hybrid rootstock were constitutively more resistant to drought, with higher efficiency in mitigating oxidative stress than ungrafted treatment. The above findings demonstrated that bitter apple, a well-adapted desert species, can be used as an alternative rootstock to commercial rootstocks (e.g., ‘Shintoza’) for watermelon grafting under water stress conditions. In addition, bitter apple rootstock can be involved in rootstock breeding programs to improve drought tolerance in watermelon.

Overexpression of \u03b3-glutamylcysteine synthetase gene from Caragana korshinskii decreases stomatal density and enhances drought tolerance

BackgroundGamma-glutamylcysteine synthetase (γ-ECS) is a rate-limiting enzyme in glutathione biosynthesis and plays a key role in plant stress responses. In this study, the endogenous expression of the Caragana korshinskiiγ-ECS (Ckγ-ECS) gene was induced by PEG 6000-mediated drought stress in the leaves of C. korshinskii. and the Ckγ-ECS overexpressing transgenic Arabidopsis thaliana plants was constructed using the C. korshinskii. isolated γ-ECS.ResultsCompared with the wildtype, the Ckγ-ECS overexpressing plants enhanced the γ-ECS activity, reduced the stomatal density and aperture sizes; they also had higher relative water content, lower water loss, and lower malondialdehyde content. At the same time, the mRNA expression of stomatal development-related gene EPF1 was increased and FAMA and STOMAGEN were decreased. Besides, the expression of auxin-relative signaling genes AXR3 and ARF5 were upregulated.ConclusionsThese changes suggest that transgenic Arabidopsis improved drought tolerance, and Ckγ-ECS may act as a negative regulator in stomatal development by regulating the mRNA expression of EPF1 and STOMAGEN through auxin signaling.

Ectopic Expression of Os-miR408 Improves Thermo-Tolerance of Perennial Ryegrass

With global warming, high temperature stress has become a main threat to the growth of cool-season turfgrasses, including perennial ryegrass. As one of the conserved plant microRNA families, miR408s are known to play roles in various abiotic stresses, including cold, drought, salinity, and oxidative stress, but no report, thus far, was found for heat. Here, perennial ryegrass plants overexpressing rice Os-miR408 were used to investigate the role of miR408 in plant heat tolerance. Both wild type (WT) and miR408 transgenic perennial ryegrass plants (TG) were subjected to short-term heat stress at 38 °C for 72 h (experiment 1) or at 42 °C for 48 h (experiment 2), and then let recover for 7 days at optimum temperature. Morphological changes and physiological parameters, including antioxidative responses of TG and WT plants, were compared. The results showed that miR408 downregulated the expression of two putative target genes, PLASTOCYANIN and LAC3. Additionally, overexpression of Os-miR408 improved thermo-tolerance of perennial ryegrass, demonstrated by lower leaf lipid peroxidation and electrolyte leakage, and higher relative water content after both 38 and 42 °C heat stresses. In addition, the enhanced thermotolerance of TG plants could be associated with its morphological changes (e.g., narrower leaves, smaller tiller angles) and elevated antioxidative capacity. This study is the first that experimentally reported a positive role of miR408 in plant tolerance to heat stress, which provided useful information for further understanding the mechanism by which miR408 improved plant high-temperature tolerance, and offered a potential genetic resource for breeding heat-resistant cool-season turfgrass in the future.

The miR169n-NF-YA8 regulation module involved in drought resistance in Brassica napus L

As an ancient and conserved plant microRNA (miRNA) family, miR169 targets nuclear factor Y subunit alpha (NF-YA) family members. The miR169-NF-YA module is associated with plant development and various stress responses. However, the function of miR169 in response to drought stress in rapeseed (Brassica napus L.) is unclear. In the present study, we showed that miR169n acted as a negative regulator of drought resistance in rapeseed by targeting a nuclear factor Y-A gene, NF-YA8. miR169n was strongly down-regulated by drought stress. Expression of a miR169n target mimicry construct (MIM169n) which functioned as a sponge to trap miR169n resulted in enhanced resistance of transgenic plants to both osmotic stress at the post-germination stage and drought stress at the seedling stage. MIM169n plants had a higher relative water content (RWC) and proline content, lower relative electrolyte leakage (REL), and showed higher antioxidative capability compared with those of control (CK) plants under drought stress. Moreover, NF-YA8 was verified as a target of miR169n, and overexpression of NF-YA8 led to improved tolerance of rapeseed to osmotic stress at the post-germination stage. Overall, our findings implied that the miR169n-NF-YA8 regulatory module could serve as a potential target for genetic improvement of drought resistance in B. napus.

Morphological, physiological and molecular assessment of cotton for drought tolerance under field conditions.

Climate change could be an existential threat to many crops. Drought and heat stress are becoming harder for cultivated crops. Cotton in Pakistan is grown under natural high temperature and low moisture, could be used as a source of heat and drought tolerance. Therefore, the study was conducted to morphological, physiological and molecular characterization of cotton genotypes under field conditions. A total of 25 cotton genotypes were selected from the gene pool of Pakistan based on tolerance to heat and drought stress. In field trail, the stress related traits like boll retention percentage, plant height, number of nodes and inter-nodal distance were recorded. In physiological assessment, traits such as photosynthesis rate, stomatal conductance, transpiration rate, leaf temperature, relative water content and excised leaf water loss were observed. At molecular level, a set of 19 important transcription factors, controlling drought/heat stress tolerance (HSPCB, GHSP26, HSFA2, HSP101, HSP3, DREB1A, DREB2A, TPS, GhNAC2, GbMYB5, GhWRKY41, GhMKK3, GhMPK17, GhMKK1, GhMPK2, APX1, HSC70, ANNAT8, and GhPP2A1) were analyzed from all genotypes. Data analyses depicted that boll retention percentage, photosynthesis, stomatal conductance, relative water content under the stress conditions were associated with the presence of important drought & heat TF/genes which depicts high genetic potential of Pakistani cotton varieties against abiotic stress. The variety MNH-886 appeared in medium plant height, high boll retention percentage, high relative water content, photosynthesis rate, stomatal conductance, transpiration rate and with maximum number transcription factors under study. The variety may be used as source material for heat and drought tolerant cotton breeding. The results of this study may be useful for the cotton breeders to develop genotype adoptable to environmental stresses under climate change scenario.

Insight into the cellular and physiological regulatory modulations of Class-I TCP9 to enhance drought and salinity stress tolerance in cowpea.

The Teosinte branched 1/Cycloidea/Proliferating cell factor (TCP) transcription factors are potent growth and developmental regulators in plants, also responsive to various hormonal and environmental stimuli. In this study, we primarily focused on the functional role of TCP9, a nuclear-localised Class-I TCP transcription factor in a drought and heat-tolerant legume crop, cowpea (Vigna unguiculata). Under drought stress, a higher protein expression level of TCP9 was observed in the leaves of the drought-tolerant cowpea cultivar Pusa Komal as compared to the drought-sensitive cultivar TVu-7778. Further, overexpression of VuTCP9 resulted in reduced cell and stomata size, aperture length and width while cell and overall stomatal density in the 35S::VuTCP9 transgenic cowpea lines increased. Phenotypic alterations, such as reduced leaf size and vigour, altered seed coats displaying extension pattern similar to the 'Watson pattern' and delayed senescence were prominent in the transgenic lines. Under normal conditions, the gas exchange and fluorescence measurements indicated reduction in transpiration rate (E), stomatal conductance (gs ) and photosynthetic efficiency (Φ PSII). However, water usage efficiency (WUE) remained unaltered in the transgenic lines as compared to the wild-type (WT) plants. Furthermore, the transgenic lines displayed higher tolerance to oxidative, drought and salinity stress, maintained relatively higher relative water content and lower occurrence of H2 O2 , as compared to the WT plants. Genes related to the jasmonic acid biosynthesis, stomatal development and abiotic stress responsiveness, such as TTG1, NAC25, SPCH and GRP1, increased and LOX2 decreased significantly in the transgenic lines.

Revegetation of coal mine degraded arid areas: The role of a native woody species under optimum water and nutrient resources

Ecological restoration of coal mine degraded soils across arid and semi-arid environments worldwide remains particularly challenging. We used a combination of greenhouse and field experiments to assess the potential role of a woody species, Ulmus pumila, in the restoration of degraded soils associated with coal-mining activities in the northwest China. We investigated how various combinations of water-nitrogen-phosphorus (W–N–P) resources affect multiple growth parameters in U. pumila. We found that several plant growth traits significantly improved with W–N applications, regardless of P inputs. Moderate-to-highest W–N–P doses increased net photosynthesis and transpiration rates, water use efficiency, stomatal conductance, chlorophyll and carotenoid contents under greenhouse conditions. A combination of high W together with low N–P applications led to high relative water content and net photosynthetic rates under field conditions. Increasing of N–P doses under W-shortage condition, aided U. pumila to enhance osmotic adjustments by increasing contents of proline and soluble sugar and also boost the activity of superoxide dismutase, peroxidase and catalase in leaf tissues to reduce accumulation of reactive oxygen species and malondialdehyde content in all conditions of greenhouse and field. Our study is the first to assess the optimum W–N–P resources in U. pumila and demonstrate that optimum growth performance could be obtained under W supplements corresponding to 90 mm year−1, N and P at 110 and 45 kg ha−1, respectively, under field condition. These findings can have far reaching implications for vegetation restoration of degraded areas associated with coal-mining activities across arid and semi-arid regions worldwide.

Physiological and transcriptomic analysis of Cabernet Sauvginon (Vitis vinifera L.) reveals the alleviating effect of exogenous strigolactones on the response of grapevine to drought stress

Drought stress can significantly affect the growth and yield of grapevine. The application of exogenous strigolactone can relieve the drought symptoms of grapevine; however, little is known about the transcription levels in grapevine under drought stress following exogenous strigolactone application. The mitigative effect of exogenous strigolactone on grapevine leaves under drought stress was studied by transcriptome analysis based on RNA sequencing. On the 10th day of drought stress, the strigolactone treatment group had a higher relative water content and lower electrical conductivity, which significantly alleviated the drought damage. Compared to the drought (D) group, a total of 5955 differentially expressed genes (DEGs) (2966 up-regulated genes and 2989 down-regulated genes) were detected in the exogenous strigolactone (DG) groups. Based on Gene Ontology analysis, the DEGs in the D and DG treatments were enriched in the processes of photosynthesis and organic acid catabolism. Pathway analysis showed that the DEGs in the D and DG treatments were enriched in carbon metabolism, ribosome, starch and sucrose metabolism, flavonoid biosynthesis, and circadian rhythm. Additionally, in the DG group, the antioxidant enzyme genes of CAT1, GSHPX1, GSHPX2, POD42, APX6, and SODCP were up-regulated, two NAC, three WRKY, and four MYB transcription factor genes were down-regulated, and the key gene of strigolactone synthesis D14 was up-regulated, compared with that in the D group. The results provide a new perspective for studying the adaptation of plants to drought stress.

Influence of Nano Silicon and Nano Selenium on Root Characters, Growth, Ion Selectivity, Yield, and Yield Components of Rice (Oryza sativa L.) under Salinity Conditions.

Rice production under salinity stress is a critical challenge facing many countries, particularly those in arid and semi-arid regions. This challenge could be handled by applying novel approaches to overcome yield limiting factors and improve resource use efficiency. The usage of nanoparticles (NPs) could be a beneficial approach to managing the growing problem of soil salinity. The aim of our study was to investigate the advantageous effects of soaking and foliar application of silicon (Si) and selenium (Se), (NPs-Si at 12.5 mg L−1 and NPs-Se at 6.25 mg L−1) on root characteristics, moropho-physiological traits, and yields of two rice varieties (i.e., Giza 177 as a salt sensitive and Giza 178 as a salt tolerant) grown in saline soil compared to untreated plants (control treatment). Results showed that soaking NPs-Se resulted in the highest value of root thickness for Giza 178 (0.90 mm, 0.95 mm) and root volume (153.30 cm3, 154.30 cm3), while Giza 177 recorded 0.83 mm, 0.81 mm for root thickness and 143.30 cm3, 141.30 cm3 for root volume in the 2018 and 2019 seasons, respectively. Soaking NPs-Se, NPs-Si and foliar application of NPs-Se at BT resulted in the highest relative water content and dry matter, while foliar application of NPs-Si at BT gave the highest leaf area index of rice plants compared to the other treatments. Giza 178 (i.e., salt tolerant variety) significantly surpassed Giza 177 (i.e., salt sensitive variety) in the main yield components such as panicle number and filled grains/ panicle, while Giza 177 significantly exceeded Giza 178 in the panicle weight, 1000-grain weight, and unfilled grains number/ panicle. Soaking NPs-Se and foliar application of NPs-Si at BT resulted in the highest grain yield of 5.41 and 5.34 t ha−1 during 2018 and 5.00 and 4.91 t ha−1 during 2019, respectively. The salt sensitive variety (Giza 177) had the highest Na+ leaf content and Na+/K+ ratio as well as the lowest K+ leaf content during both seasons. Applying nano nutrients such as NPs-Si and NPs-Se improved the yield components of the salt sensitive variety (Giza 177) by enhancing its ion selectivity. Both NPs-Si and NPs-Se had almost the same mode of action to mitigate the harmful salinity and enhance plant growth, and subsequently improved the grain yield. In summary, the application of NPs-Si and NPs-Se is recommended as a result of their positive influence on rice growth and yield as well as minimizing the negative effects of salt stress.

Correlation of stress indices with yield parameters in wild chickpea (Cicer arietinum L.) accessions under irrigated and rainfed conditions

Six wild chickpea accessions were procured during Rabi seasons 2015-16 and 2016-17 seasons at Punjab Agricultural University, Ludhiana to record morpho-physiological parameters and yield components at pod initiation stage. The experiment was carried out in randomized block design with two treatments irrigated and rainfed each with three replicates. Results indicated a significant decrease in the specific leaf weight (SLW), photosynthetic rate (PR) and relative water content (RWC) under rainfed conditions in wild chickpea accessions. Wild accessions C judaicum 17148 (29.5%) and C pinnatifidum212 (31.0%)displayed their resistance towards water scarcity by maintaining high relative water content that depicted negative correlation with membrane damage (r=-0.98).The membrane damage showed an inversely proportional relationship (r=-0.69) with seed weight, a yield component under rainfed conditions evidencing the requirement of water at pod filling stage.

Physiological and Molecular Responses of Six Apple Rootstocks to Osmotic Stress.

The growth and productivity of several apple rootstocks have been evaluated in various previous studies. However, limited information is available on their tolerance to osmotic stress. In the present study, the physiological and molecular responses as well as abscisic acid (ABA) levels were assessed in six apple rootstocks (M26, V3, G41, G935, B9 and B118) osmotically stressed with polyethylene glycol (PEG, 30%) application under greenhouse conditions. Our results showed that V3, G41, G935 and B9 had higher relative water content (RWC), and lower electrolyte leakage (EL) under stress conditions compared to M26 and B118. Additionally, water use efficiency (WUE) was higher in V3, G41 and B9 than M26, which might be partially due to the lower transpiration rate in these tolerant rootstocks. V3, G41 and B9 rootstocks also displayed high endogenous ABA levels which was combined with a reduction in stomatal conductance and decreased water loss. At the transcriptional level, genes involved in ABA-dependent and ABA-independent pathways, e.g., SnRK, DREB, ERD and MYC2, showed higher expression in V3, G41, G935 and B9 rootstocks compared to M26 in response to stress. In contrast, WRKY29 was down-regulated in response to stress in the tolerant rootstocks, and its expression was negatively correlated with ABA content and stomatal closure. Overall, the findings of this study showed that B9, V3 and G41 displayed better osmotic stress tolerance followed by G935 then M26 and B118 rootstocks.

Effect of oxalic acid on vase life and antioxidative activities of ‘Mero Star’ cut lily flowers

Lily (Lilium L. hybrids) is sub-tropical cut flower that can be grown in open place or in green house and has consumer demand in local as well as in offshore markets. Short vase life, postharvest decay of flowering petals, activities of oxidative enzymes, malondialdehyde contents, electrolyte leakage and low water ratio are the main problems in marketing of cut lilies. This study was carried out to investigate the effect of oxalic acid (OA) treatments on vase life (12 days) and postharvest quality of ‘Mero Star’ cut lily flowers. The flowering stems were placed in 2, 4 and 6% aqueous solution of OA for 12 days at 20±2 °C with 70±5% relative humidity. Flowers placed in 6% OA solution exhibited longest vase life and flower diameter with higher relative water content and increased fresh weight and reduced flower decay. Reduced malondialdehyde contents and electrolyte leakage with higher activities of catalase, superoxide dismutase and peroxidase enzymes were also noted in 6% OA-treated flowers. In conclusion, exogenous postharvest application of 6% OA extended vase life and maintained postharvest quality of cut flowers by reducing electrolyte leakage and malondialdehyde contents with higher antioxidative enzymes activities.

Effect of salicylic acid and progesterone on physiological characteristics of Kentucky bluegrass under salinity stress

Salinity is one of the most important limiting factors in plant growth. It is also a predominant constraint that impairs grass growth and quality. Plant hormones play important roles in the capability of plants to adapt to environmental stresses. Hence, the impact of two plant growth regulators (PGRs) i.e. salicylic acid (SA) and progesterone (P4) was studied on biological characteristics of Poa pratensis in saline conditions in a greenhouse experimnt. The experimental treatments were composed of salinity at four levels (0, 2, 4, and 6 dS m-1) and six levels of PGRs (control, 1 mg L-1 P4,10 mg L-1 P4, 1 mM SA, 3 mM SA, and 1 mg L-1 P4 + 1 mM SA). The results showed that leaf firing percentage was increased with the excess in salinity, but the use of SA and P4 eased the effects of salinity stress and reduced leaf firing under salinity. 6 dS m-1 and 3 mM SA salinity caused to the maximum electrolyte leakage. The highest relative water content was observed in 4 dS m-1 salinity and 1 mM SA treatment. The highest glycine betaine was related to 6 dS m-1 NaCl and no hormone application. Salinity increased total protein and catalase, and the simultaneous use of P4 and SA exhibited the highest total protein and catalase content, whilst the control plants showed the lowest ones. The application of salinity stress reduced chlorophyll content, but SA and P4 increased it. The application of the two growth regulators improved carotenoid content under salinity stress. Overall, the results showed that the application of SA and P4 improved salinity tolerance and increased pigments and antioxidant enzyme activities.

Tolerance mechanisms in maize identified through phenotyping and transcriptome analysis in response to water deficit stress.

The online version contains supplementary material available at 10.1007/s12298-021-01003-4.

Assessment of flag leaf water status as drought tolerance discriminating trait in durum wheat (Triticum turgidum var durum L.)

Drought is a prominent limiting factor that impacts negatively durum wheat grain yield. Ten durum wheat breeding lines were evaluated under rainfall conditions at the Field Crop Institute Agricultural Experimental Station of Setif, Algeria, during the 2016/2017 cropping season. The investigation aimed to study the ability of flag leaf water status to discriminate among varieties for drought tolerance trait. Significant variability was observed among the tested varieties for leaf dry, wilted and turgid weights, leaf relative water content, water saturation deficit and excised water loss, after three wilting periods of 30, 60 and 90 minutes dehydration at 40°C. The assessed breeding lines were differentially categorized as drought tolerant and drought sensitive based on either relative water content or water saturation deficit or excised leaf water loss genotypic mean values. Correlation, principal components and cluster analyses indicated an unwanted significant association between excised leaf water loss and relative water content and water saturation deficit and classified the assessed entries into three clusters (CI, C2 and C3). Cluster C1 had high relative water content, low water saturation deficit but high excised water loss, while C3 had low relative water content, low excised leaf water but high-water saturation deficit, C2 being intermediate. Crosses between distant clusters (C1 vs C3) are proposed to generate more variability of the targeted traits in progeny population and to break undesirable linkage between alleles controlling leaf water status, allowing to select efficiently drought tolerant genotypes.

Role of kaolin on drought tolerance and nut quality of Persian walnut

Global warming has endangered crop production by reducing water availability and increasing temperature. Kaolin may protect plants against these conditions by reflecting the light and decreasing plant temperature. This study was conducted to evaluate the protective effects of kaolin spraying on kernel yield and quality of four walnut cultivars and genotype. The experiment was conducted as a split-plot factorial design in time factor with four factors including irrigation levels (100% and 50% of regular irrigation), kaolin solution concentrations (0, 2.5, 5 and 7.5%), walnut varieties (‘Chandler’, ‘Franquette’, ‘K72’ and ‘SG’) in two consecutive years (2012–2013). By increasing the kaolin concentration under well-watered irrigation, gas exchange, chlorophyll concentration, leaf potassium content, and kernel quality were improved. Moreover, increasing the kaolin concentration reduced sunburn and leaf temperature under different irrigation regimes. Based on results, genotypes ‘K72’ and ‘SG’ showed more severe sunburn symptoms. Water stress and no kaolin application had negative effect on the kernel color. Leaf temperature increased with reducing the irrigation and concentration of kaolin. Under water stress, ‘Chandler’ had the highest relative water content (58.25%) and ‘Franquette’ had the lowest RWC and therefore considered as the most drought sensitive cultivar. The lowest fruits sunburn in ‘Franquette’, was related to the thickness of its fruits’ husk. In general, the foliar application of kaolin 5% and 7.5% alleviated the negative effect of drought stress and improved the walnut kernels quality under water deficit condition by improving chlorophyll content, RWC, and gas exchange and reducing leaf temperature.

Physiological, developmental and growth responses to desiccation induced stress in four seed coat colour varieties of Vigna unguiculata (L. Walp).

Cowpea (Vigna unguiculata L. Walp) is a widely grown leguminous crop in Ghana. This study was conducted using four varieties of cowpea based on the colour of the seed coat namely; red, brown, black and cream cowpea varieties, and were subjected to three different watering regimes, namely: Normal, moderate and severe water stress regimes. These different watering regimes were used as potential screening criteria to determine their drought tolerance ability. We monitored changes in physiological, morphological and yield traits due to the effects of four seed coat colour varieties and imposed water regimes. The effects of seed coat colour on relative water content (RWC) was significant (F = 13.15; p ≤ 0.05). Red variety recorded the highest RWC (60.14%) with the lowest RWC (50.71%) in the Black seed colour, all under severe water stress. The Red and Cream seed coats had a soil moisture content (SMC) of 62.61 and 48.70% respectively when the severe water stress treatment was considered. There was a decreasing trend in chlorophyll content for all four cowpea varieties. The Brown and Red varieties recorded the highest chlorophyll contents under moderate and severe water stress respectively. Proline concentrations were high with increasing drought severity. The Red cowpea variety recorded the maximum concentration of free proline (5.7 µg/g) under severe water stress. Mean seed weight in Red seed coat, subjected to severe water stress, was 0.48 g. Results in this experiment revealed that the Red seed coat colour appeared to be tolerant to severe water stress compared to Cream, Black and Brown seed coats. Key words: Cowpea, seed coat colour, water stress, relative water content, soil moisture content.